The 278 illnesses in 18 states were believed to be linked to raw chicken from three Foster Farms locations in California, according to the Food Safety Inspection Service.
"The outbreak is still ongoing, and therefore our investigation is still ongoing," a spokesman for FSIS told AFP on Wednesday.
The shutdown, which began October 1, has sent hundreds of thousands of federal workers home without pay, including staff at the Centers for Disease Control and Prevention, Department of Agriculture and Food and Drug Administration.
It is the first shutdown in 17 years and was driven by a resurgence of Republican opposition to President Barack Obama's healthcare reform law passed in 2010.
The FDA has warned it would "be unable to support the majority of its food safety, nutrition, and cosmetics activities."
"The shutdown has really handcuffed these regulatory agencies and their proper regulatory role," Eric Walker, spokesman for Congresswoman Louise Slaughter, told AFP.
"This is the nightmare scenario, not just with the government shutdown but this is what happens when you overuse antibiotics in livestock."
A high proportion of people have been hospitalized -- 42 percent -- and some of the salmonella strains are showing resistance to antibiotics, according to the Center for Science in the Public Interest.
The consumer advocacy group also noted that seven strains of salmonella appear to be responsible for the sicknesses.
"The number of people we know to be ill is just the tip of the iceberg," said CSPI food safety director Caroline Smith DeWaal.
"This outbreak shows that is a terrible time for government public health officials to be locked out of their offices and labs, and for government Web sites to go dark."
The FSIS warned that salmonella infections "can be life-threatening, especially to those with weak immune systems, such as infants, the elderly and persons with HIV infection or undergoing chemotherapy."
Common symptoms include diarrhea, stomach cramps and fever within eight to 72 hours of consuming infected food. Illness including nausea, chills and headache may persist for up to a week.
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